1. Field of the Invention
The invention relates to a feed velocity control apparatus for the velocity control of an information reading point for use in a disc player for reproducing recorded information from a recording disc.
2. Related Background Art
Various discs, such as CD, DVD, MD, MO, hard disk, or the like are put into practical use as optical, magnetooptic, or magnetic information recording discs (hereinafter, simply referred to as recording discs).
In a disc player for reproducing information data from the recording disc, a velocity servo operation is performed to control a feed velocity of a pickup in the disc""s radial direction in order to move an information reading point of the pickup to a desired recording position (on the disc""s recording surface) at a high speed. The velocity servo is a technique for controlling the feed velocity of the pickup so that a predetermined velocity of the information reading point is attained by using a tracking error signal that is obtained when the information reading point of the pickup traverses recording tracks formed on the recording surface of the recording disc.
More specifically, the first step is to binarize the tracking error signal which is obtained at the time of a track jump based on a predetermined threshold value. This generates a track crossing signal whose logical level changes in a way xe2x80x9c1xe2x80x9dxe2x86x92xe2x80x9c0xe2x80x9dxe2x86x92xe2x80x9c1xe2x80x9d (or xe2x80x9c0xe2x80x9dxe2x86x92xe2x80x9c1xe2x80x9dxe2x86x92xe2x80x9c0xe2x80x9d) each time the information reading point transverses the recording tracks. The pulse width of the track crossing signal corresponds to a sum of velocities obtained by adding a transporting velocity of a slider at the present time point and a velocity at which the information reading point is moved by a tracking actuator. That is, the information reading point is moved at a low speed when the pulse width of the track crossing signal is long and transported at a high speed when the pulse width is short.
Therefore, by performing a velocity servo operation to the slider and the tracking actuator in such a manner as to decelerate them when the pulse width of the track crossing signal is short and accelerate them when it is long, the transporting velocity of the information reading point at the time of the track jump can be controlled so as to attain a predetermined velocity.
However, when an amplitude level of the tracking error signal decreases due to a scratch or the like formed on the disc recording surface, the track crossing signal drops for such a period of time. Consequently, the pulse width of the track crossing signal becomes long irrespective of the moving velocity of the information reading point at the present time point and the slider and the tracking actuator are excessively driven than they are needed in order to settle the velocity servo. Even if the pulse width of the track crossing signal is subsequently returned to the normal state, therefore, it is difficult to promptly settle the velocity servo system and a problem arises that the stable constant velocity control is not performed. An erroneous pulse train irrespective of the tracking error signal is multiplexed to the track crossing signal due to an influence of noises or the like, so that a similar problem occurs also in cases where the pulse width of the tracking error signal becomes unusually short.
The invention has been made to solve the problems and it is an object to provide a feed velocity control apparatus for a velocity control of an information reading point in a disc player which can perform a stable velocity control by reducing influences of scratches formed on a recording surface of a recording disc, noises, or the like.
According to the invention, there is provided a feed velocity control apparatus for a velocity control of an information reading point of a disc player which comprises an information reading device for reading recording information from recording tracks formed on a recording disc thereby obtaining a read signal, and a moving device for moving the information reading point of the information reading means in the direction which transverses the recording tracks, the apparatus comprising: tracking error generating means for generating a tracking error signal based on the read signal; velocity signal generating means for generating a velocity signal corresponding to a transporting velocity of the transporting means on based on the tracking error signal; velocity error signal generating means for generating a velocity error signal corresponding to a difference between the velocity signal and a predetermined velocity at the time of a track jumping operation of the information reading means; a low pass filter for obtaining a velocity error low band signal by extracting a low band component of the velocity error signal; and constant velocity control means for driving the moving device in accordance with the velocity error signal when the velocity signal lies within a predetermined velocity range at the time of the track jumping operation of the information reading means and driving the moving device in accordance with the velocity error low band signal in place of the velocity error signal when the velocity signal is out of the predetermined velocity range.